Membrane proteins play vital roles in all living systems. Approximately ˜30% of all genes in almost all sequenced genomes, code for membrane proteins. However, our detailed understanding of their structure and function lags far behind that of soluble proteins. As of February 2012, there are over 79,500 structures in the Protein Data Bank (http://www.resb.org/pdb/home/home.do), however, there are 952 membrane protein structures with 320 unique structures including 8 G-protein coupled receptors. Although there are about 400 functional olfactory receptors in human, not a single olfactory receptor has been determined.
There are several bottlenecks in elucidating the structure and function of olfactory receptors and their recognition and odorant-binding properties although they are of great interest. The most critical and challenging task is that it is extremely difficult to produce milligrams quantities of soluble and stable receptors. Inexpensive large-scale production methods are desperately needed, and have thus been the focus of extensive research. It is only possible to conduct detailed structural studies once these preliminary obstacles have been surmounted. Therefore, there is a need in the art for improved methods of studying G-protein coupled receptors, including olfactory receptors.